The present invention relates to a multilayer printed wiring board having a plurality of wiring pattern layers and many plated through holes for mounting electronic elements, such as LSI (large scale integrated circuits), IC (integrated circuits) or transistors.
The wiring patterns of a multilayer printed wiring board are sometimes required to be changed after electronic elements are mounted on the printed wiring board. In a multilayer printed wiring board according to the prior art, if it is necessary to cut the electrical connection between a terminal of an electronic element on the board and the patterns, the cutting operation is achieved by removing the elements from the board and then cutting the wiring patterns or breaking the plated through hole into which the terminal is inserted by drilling.
FIG. 1 is a sectional view of a multilayer printed wiring board according to the prior art. An electronic element 2 is mounted on a multilayer printed wiring board 4 according to the prior art. Each terminal 3 of the electronic element 2 is inserted into a different plated through hole A, B, C or D. Four layers of a wiring pattern 1 are printed in the board 4. When it is necessary to cut the electrical connection between one of the terminals 3, for example the terminal 3 in the plated through hole B, and the patterns 1, the cutting operation is achieved as follows. At first, the electronic element 2 is removed from the printed wiring board 4. Then the plated through hole B is broken and enlarged by a drill to cut the patterns 1 at the plated through hole B. Then the plated through holes A and C are connected discretely by a lead wire 5 (FIG. 2). Then the electronic element 2 is mounted again on the board 4 by inserting the terminals 3 into the plated through holes A, B, C, and D, respectively. As a result, the electrical connection between the terminal 3 in the plated through hole B and the patterns 1 is eliminated.
However, the above-mentioned cutting operation, especially the drilling and the connecting of the lead wire with solder, requires a great amount of time and care.